1. Field
Embodiments relate to a nanocrystalline diamond thin film and a method for fabricating same. More particularly, embodiments relate to a uniform nanocrystalline diamond thin film with minimized voids formed on a silicon oxide-coated substrate and a method for fabricating the same. Such nanocrystalline diamond thin film is formed by performing hydrogen plasma treatment, hydrocarbon plasma treatment or hydrocarbon thermal treatment on the substrate surface to maximize electrostatic attraction between the substrate surface and nanodiamond particles during the following ultrasonic seeding such that the nanodiamond particles are uniformly distributed and bound on the silicon oxide on the substrate.
2. Description of the Related Art
The nanocrystalline diamond (NCD) or ultrananocrystalline diamond (UNCD) thin film has opened an innovative route for a wide variety of applications. In particular, nanocrystalline diamond (less than 100 nm in thickness) formed on a silicon oxide (SiO2)— coated silicon (Si) substrate is important for nanoelectromechanical system (NEMS) applications. Also, the nanocrystalline diamond thin film is used as a hermetic coating over the 3-dimensional geometry of the microelectrode arrays for implanted retinal prosthesis or as a dielectric layer of a localized surface plasmon resonance (LSPR) sensor.
Meanwhile, it is very difficult to grow a void-free nanocrystalline diamond thin film on the silicon oxide surface due to low nucleation density and long pretreatment time when compared to the growth on the pristine silicon substrate (Bhattacharyya, S.; Auciello, O.; Birrell, J.; Carlisle, J. A.; Curtiss, L. A.; Goyette, A. N.; Gruen, D. M,; Krauss, A. R.; Schlueter, J.; Sumant, A.; Zapol, P. Applied Physics Letters 2001, 79, 1441.).
When a hydrogen-rich, rather than argon (Ar)-rich, precursor gas is used to grow the nanocrystalline diamond thin film, the nucleation rate is decreased due to the etching action of the high-concentration hydrogen. Nonetheless, hydrogen-rich precursor gas is still prevailing for nanocrystalline diamond synthesis due to better plasma stability in microwave plasma chemical vapor deposition (MWCVD) or direct current plasma-assisted chemical vapor deposition (DC-PACVD) or due to a much wider gas composition window in hot filament chemical vapor deposition (HFCVD).
Bias enhanced nucleation (BEN) technique has been widely adopted for enhancing nucleation for diamond synthesis on a silicon substrate. However, although it is appropriate for an electrically conducting substrate, the technique is not suitable for a non-conducting substrate such as an oxide-coated substrate and is limited in large-area diamond deposition.
Ultrasonic treatment of a substrate immersed in a diamond powder suspension is also widely adopted for nucleation enhancement. Initially, it was argued that the nucleation was enhanced by scratching on the substrate surface by microdiamond particles when the suspension of microdiamond particles was used for ultrasonic treatment. It was subsequently discovered that the diamond particles remaining on the substrate was responsible for the enhancement of nucleation.
By contrast, for growth of the nanocrystalline diamond thin film, a suspension of nanodiamond particles is used. The nanodiamond particles are transferred from the suspension to the substrate by ultrasonic seeding. In this context, various efforts were made to enhance the dispersion efficiency of the nanodiamond particles onto the substrate, including functionalization of the seed particle surface, addition of a surfactant to the suspension or adjustment of the pH of the suspension. Furthermore, ball-milling of the nanodiamond particles using ceramic beads or thermal treatment of the nanodiamond particles under hydrogen atmosphere is also employed to increase the dispersion efficiency of the nanodiamond particles.
However, such efforts are directed exclusively to the diamond particles, not to the substrate onto which the diamond particles are transferred.